The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for manufacturing a semiconductor device, which is capable of reducing a parasitic bit line capacitance due to an increase in a thickness of a barrier film of a bit line.
Bit lines in a semiconductor memory device such as a dynamic RAM (DRAM) supply current through a channel for storing electric charge in the memory capacitors and transfer differing amounts of electric charges between capacitors to a sense amplifier so that the electric charges stored in the capacitors can be converted into data. Typically, the bit lines were formed using a Ti/TiN barrier film and a tungsten conductive film.
Hereinafter, a method for forming the conventional bit line contact plug and the bit line using the tungsten film as a bit line material will be briefly described.
After an interlayer insulation film is formed over upper portion of a semiconductor substrate formed with a desired base structure, the interlayer insulation film is etched to form a hole for a bit line contact plug. Ti/TiN film is formed as a barrier film over the interlayer insulation film including the surface of the hole. A tungsten film is formed as a conductive film over the barrier film to fill the hole. A hard mask made of a nitride film defining a bit line forming area is formed on the tungsten film.
The conductive film and the barrier film are etched using the hard mask as an etching mask to form a bit line contact plug in the hole and also to form a bit line over the interlayer insulation film such that the bit line is in contact with the bit line contact plug.
The conductive film serves to transfer most of the electric flows when the semiconductor is operating, and the barrier film serves to improve the contact resistance and protects the junction area by inhibiting chemical reaction between the tungsten film and any of the base structure during the deposition of the tungsten film.
However, the thickness ratio of the barrier film and the conductive film has reached to almost 1:1 when fabricating a highly integrated semiconductor device, causing various problems.
A conventional bit line structure in a semiconductor device, for example, has a bit line contact plug and a bit line 130 including a barrier film and a conductive film respectively, and the thickness for each of the barrier film and the conductive film is almost same.
When the thickness for each of the barrier film and the conductive film is almost same, the subsequent photo and etching processes are difficult to carry out, and the parasitic capacitance of the semiconductor increases, thereby degrading the device properties and lowering the production yield.